Python Debugger Suggestions

[nilamo]

https://python-forum.io/Thread-MySql-Cur...7#pid61337

tbh I highly dislike that the most common way to debug an application is to print variables out. Does anyone use a debugger? Perhaps with breakpoints, variable inspections, the ability to modify variables from a breakpoint and continue with the new values, etc?

[ichabod801]

What about pdb? I haven't tried it, but it comes with Python.

[nilamo]

Ok, that's actually pretty good, but super hard to figure out how to use. Let's start with a broken file to test:

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def fails(test: int = 7) -> str:     x = 42     assert x == test     if __name__ == '__main__':     print(fails())

Proof that it's broken:

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>python spam.py Traceback (most recent call last):   File "spam.py", line 7, in <module>     print(fails())   File "spam.py", line 3, in fails     assert x == test AssertionError

Debug (run until error, set a breakpoint, check values at that breakpoint, and set a local variable to fix issue, then continue running):

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E:\Projects\etc>python -m pdb spam.py > e:\projects\etc\spam.py(1)<module>() -> def fails(test: int = 7) -> str: (Pdb) continue Traceback (most recent call last):   File "E:\ProgramFiles\Python37\lib\pdb.py", line 1697, in main     pdb._runscript(mainpyfile)   File "E:\ProgramFiles\Python37\lib\pdb.py", line 1566, in _runscript     self.run(statement)   File "E:\ProgramFiles\Python37\lib\bdb.py", line 585, in run     exec(cmd, globals, locals)   File "<string>", line 1, in <module>   File "e:\projects\etc\spam.py", line 1, in <module>     def fails(test: int = 7) -> str:   File "e:\projects\etc\spam.py", line 3, in fails     assert x == test AssertionError Uncaught exception. Entering post mortem debugging Running 'cont' or 'step' will restart the program > e:\projects\etc\spam.py(3)fails() -> assert x == test (Pdb) list   1     def fails(test: int = 7) -> str:   2         x = 42   3  ->     assert x == test   4   5   6     if __name__ == '__main__':   7         print(fails()) [EOF] (Pdb) break 2 Breakpoint 1 at e:\projects\etc\spam.py:2 (Pdb) continue Post mortem debugger finished. The spam.py will be restarted > e:\projects\etc\spam.py(1)<module>() -> def fails(test: int = 7) -> str: (Pdb) continue > e:\projects\etc\spam.py(2)fails() -> x = 42 (Pdb) p x *** NameError: name 'x' is not defined (Pdb) p test 7 (Pdb) !test = 42 (Pdb) p test 42 (Pdb) continue None The program finished and will be restarted > e:\projects\etc\spam.py(1)<module>() -> def fails(test: int = 7) -> str: (Pdb) exit

So it definitely works, but is loaded with magic incantations to work right. Maybe that's because I'm not used to command-line debuggers lol.

[jdjeffers]

Now you know about the debugger, it's just a matter of using it.

Before you know it, you'll be writing tests, too.